The present invention relates to a portable display apparatus and, more particularly, to a display apparatus designed to be mounted on the user's head to observe an electronic image or the like.
There has heretofore been proposed a head-mounted display apparatus which enables an electronic image displayed on a liquid crystal display device to be viewed superimposed on an outside, real world image (see Japanese Patent Application Laid-Open (KOKAI) No. 03-191389 (1991)). The conventional display apparatus is arranged as shown in FIG. 10. A half-mirror 1 is obliquely disposed in front of an observer's eye, and a liquid crystal display device 2 is disposed off the observer's visual axis so that display light from the liquid crystal display device 2 is incident on the half-mirror 1. In addition, a concave mirror 3 is disposed to face the liquid crystal display device 2 across the half-mirror 1.
Accordingly, a part of the light from the liquid crystal display device 2 is transmitted by the half-mirror 1 and reflected by the concave mirror 3, and a part of the reflected light is reflected by the half-mirror 1 to reach the observer's eye. At the same time, a part of light from the outside world is also transmitted by the half-mirror 1 to reach the observer's eye. Accordingly, the observer can see both an enlarged electronic image from the liquid crystal display device 2 and an outside, real world image, which are superimposed on one another.
In this type of conventional display apparatus, however, the brightness of the electronic image observed is a quarter of that of the original electronic image because the display light passes through the half-mirror 1 twice before reaching the observer's eye. Therefore, the display efficiency is low. In addition, it is impossible to vary the brightness of the outside, real world image or to shut out light from the outside world.